Pylonracr

Yo, dude with the way too cool avitar...

The prop is an Eliminator 7 3/8 x 7 1/2 Carbon. He makes several in that general range. That is the first one I grabbed and put on and it seemed fairly happy. I am building a plane for it now, so I will probably try a few more. I love that engine. I have wanted one since I heard that he made some back in the ducted fan days. I found a member that was selling one, so I paid too much for it, sent the rear rotor assembly and piston/sleeve to Dub and told him to do what it needs to be perfect and send an extra piston and sleeve. I now have a fresh engine and a spare rebuild.

The resin I use on the pipes is an Aeropoxy product that has a Tg of around 400F. I have not had any issues yet, as the pipes seem to get enough cooling air to keep them from melting. I have never had one get soft on the test stand during a bench run, and they seem to last on the planes.

Out of curiosity, what is an average running temp on an F3D pipe?

Scott

Pylonracr

I think I sent you a carbon pipe for a big block fan engine? I thought I remembered you telling me that it made a few hundred more rpm than the aluminum pipe but you broke the inlet with a clamp?? If you want to send it back down I will fix it for you. What engine are you going to use in the Macchi? I may be able to come up with a suitable pipe for you..

If I remember correctly, you were going to make some 9 x 11 or 9 x 12 carbon props??

Scott

Rudeboy

I was going to say, watch out with APC Q40 props...they do fly apart every once in a while.
But carbon is top notch 👌

I Haven't measured pipe temps, but I know they sometimes get hot enough to burn away the burnt castor oil on the header section...Let's say the first 3-4 inches right behind the engine.

The barstock pipes I use have fins milled into the header section, for cooling.
Because the pipes tended to fail there because the aluminum got too hot...

The pistons get bloody hot too, there is burnt castor on the inside of the piston after a few runs.

MJD

My Feedback: (1)

I run the very same prop on my OPS .45 DF engines. The 85% dia trimmed bench version turns 26.5k static.

MJD

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Yeah, for my OPS .65. Ran like a bear but the first 2-3" got cooked a bit. I'd be happy to send it down for forensics.

I made an executive decision on the engine, decided to use an OS .91 VRDF set up for a 10-10 or 10-9 APC carbon prop. Recent bench run here: The engine ought to hold up for enough flights at that stress level, and it will be a fine sport flier. I'd like to invert it and tuck the pipe under the fuse, need to find one of those Rossi 40402 headers to fit, their header inlets are the correct diameter. This is a big fat muffled 15cc pipe of random origin (classifieds goodie box..), must be a MAC though.

Rudeboy

These are probably less than 15 runs old...

MJD

My Feedback: (1)

OK, what am I seeing here and under what conditions? I was advised that keeping the rpm under 20k would do a lot to keep the engine together. Am I wasting my time?

p.s. no wonder your handle is rudeboy, look where you're holding those pistons.

Rudeboy

Those are a couple of scrap MB40 pistons.
They are no good, because the hole for the piston pin is elongated on the exhaust side.

As for your 90 VRDF...it should live forever at that rpm. That's basically half throttle for these things.

Pylonracr

I have heard that as well. 18 to 19K keeps the rod happy. Make sure you run 20% oil.

MJD

My Feedback: (1)

Yeah I don't typically run fuel out of the jug in the propped DF engines, I always bring total oil up to 22-23%, and don't need a lot of nitro to go fast enough for _hits and giggles. I use SIG Champion 20% oil 50/50 cas/syn in various nitro % in high end 1/2A's and some other small engines, and for Coxes and any other castor-hungry 1/2A's lately I take car fuel and bring total oil up to 23% with castor. I run Omega out of the jug in $79.95 sport engines though.

The .91 is making a bit better than 3.5hp at 17k, so that's acceptable for sport flying.

MJD

My Feedback: (1)

I measured up the pipe, I would say it is a .90-.120 muffled marine pipe (came in a goodie box). The inlet is 3/4" ID, max OD is 2.25", and it has a 2" section at full diameter before the converging cone. And it is frigging heavy. At these rpm I wonder if there may be more boost from a 10cc pipe?

Pylonracr

I would try a 10cc pipe on it. You already have a baseline. My 10cc carbon pipe is slightly larger than a MACS pipe, but very similar. Did you ever get a set of carbon wingtips from Shawn for the Macchi? If not I have a set I can send you.

Scott

MJD

My Feedback: (1)

LOL, I was toying with mentioning those tips just for fun! I never did get them, no, but he did have them supposedly ready to ship at one point. I suppose if there was a time to get them it would be now. No panic, that won't hold me back yet. I will send the pipe down asap, if there are any Covid bugs on it, they should die by the time you get it. The smell will do the trick I think.

I am trying to find the PM or post where you passed on some info on the model.. such as the nose plate being at 0-0 for reference on stab alignment, using 15 size retracts etc.. that is all from memory though. Also, did you or Shawn say there are balsa insets for the wing TE/aileron LE? Or is it just open foam and I cut out the ailerons and cap them and the bays? There was nothing with the model just the bits, not that general construction isn't obvious of course. I dug up a Macchi top view and scaled out the tail group location from that - the relative location looks just like the photos of the bright red one to me. Dang it is a sharp looking model.

Yeah I'll run it up with a 10cc open pipe, I don't have a proper muffled 10cc pipe. Now I'll have to find my ear protectors. I have OPS Super .60 pipes for pattern, but those are essentially 7.5cc size pipes with mufflers, and deal with um, er.. about 60% or so? of the gas flow of the .91 setup.

Pylonracr

OK Mike, here goes. I was never really involved in the building of the plane, pretty much all I did was mix the fuel for it. That being said, I have some answers for you. The wings are sheeted foam cores, the skins are 1/16 balsa, with 1/8 x 1/4 balsa spars. Shawn and I do the spars a little differently, I take the balsa spar and laminate a layer of 12K carbon tow top and bottom, put it in the slot, and laminate the skin to it. Vacuum bag of course. Make darn sure that the spar is level or a tad proud of the surface of the foam so it gets glued to the skin. Where the ailerons go, laminate some 1.7 ounce Kevlar, cut on the bias, between the core and the top skin. This is the live hinge when you cut the ailerons loose from the wing. No hinging necessary. Not sure if the tail is sheeted cores or not. You will have to hit Shawn up for the retracts, I know he used some light inexpensive electrics with very good results, but I am not sure what they were. Be sure and tell him that after waiting 4 years for the wingtips you never received that you got a set from me.... I will pm you Shawns contact info. Any question on the live hinges hit me up and I will explain in more detail.

Scott

MJD

My Feedback: (1)

Thanks Scott. I thought it was you who had written that before, memory is a soluble thing. I'll get hold of Shawn - thx.

My cores are pre-sheeted, the retract bays are in, it has a laminated vertical grain wing joiner. The stabs are vac-bagged balsa. This will be a very light aircraft.. looking forward to that part.

MJD

My Feedback: (1)

I ran up the OS .91 on a slightly smaller pipe, 1.75" OD versus the 2.25" pipe. I think it is a 15cc marine pipe. Tweaked length up and down a bit, but still lost about 200 rpm on the top - was expecting at least the same rpm.

Rudeboy

Not enough volume?
Could be a number of things though.

Pylonracr

200 RPM could be atmospheric as well. Hotter day with a tad thinner air? 200 is not much..

Scott

MJD

My Feedback: (1)

Yeah, could be, it was colder on the earlier runs. Also, saving a few ounces of pipe weight is worth a few rpm.. so obsessing is not likely necessary.

Rudeboy

I have no experience with 90 marine pipes and such, I only have F3D....but pipes have a massive impact on how your 2 stroke runs.
Head volume (compression) is the second thing when you change pipes.

Some pipes mandate low compression, while others like the opposite

MJD

My Feedback: (1)

FYI I compared the carbon pipe to my OS .77 stock pipe - they are remarkably similar in profile,the only difference I could see was that the convergent cone is a bit shorter because it terminates in a larger ID stinger.

dhal22

Nice to catch up here and read experienced speed addicts posts.

MJD

My Feedback: (1)

Since I did not plan to run my OS .77 at full tilt either (and would thus need to put together a longer pipe package for it anyways), I cut off the integral adapter and mated the pipe to a Rossi 10cc offset header at 33cm length from plug - peak diameter. The .91 VRDF is back to 17,100 on the stand with APC 10X10C and the pipe setup is very light as well. It starts very much like a sport engine, a casual backflip of the prop when the cylinder is wet, and off it goes. Sure eats fuel. I cranked it rich on one run and swear I could see the tank level dropping, as it generated enough oil smoke to fog an orchard. So I am content with this setup for the Macchi 202, I suspect it will end up as an amusing 150-160 sport machine. And I can retrofit it with the CF pipe down the road once sorted.

Pylonracr

17K with a 10 x 10 is pretty healthy. I think you will be happy with that. As long as it will transition, the engine will last at a flight RPM of mid 18's to low 19's. Let me know if you need some wing tips....

Scott

MJD

My Feedback: (1)

I would love those wing tips. Happy to pay you for them. Shawn will owe me of course.. :-). I found the receipt where I sent it LOL.

I spotted a note where I think it was Shawn commenting that he didn't have much luck with 9" props on the Macchi. Looking at the airframe, I can see that but I tend to think 10" is plenty of disc area.

Yeah the engine hops up on the pipe without any trouble, and has a range of adjustment when on the boil, so for pure speed I could likely shorten a hair more, but for sport flying and horsing around I think this is where it wants to be and it's not a speed model anyways - just a brisk model. The engine runs relatively cool and fuss-free, it sounds content to my ears. I haven't taken out a plug on the bench yet, either I've been lucky or haven't been pushing it that hard. I've needled past peak and back again several times but only transient.

I am, however, going with the less aerodynamic but simpler side mounting. Finding headers bla bla.. I already had the Rossi offset that will work fine side mounted. Nowhere near as elegant as enclosed pipes venting behind the cockpit, but I'll get it done..